1. Technical Field
Embodiments are generally related to single staged refrigeration systems, and more particularly to single staged refrigeration systems used in but not limited to residential air conditioning systems, roof top units, residential and commercial air source heat pumps and water source heat pumps.
2. Discussion of Prior Art
Single staged refrigeration systems are widely used in both residential and commercial buildings. Typical systems maintain single zone room temperatures by staging a compressor on and off. These systems have a supply air fan with ON and AUTO modes of operation. The fan ON mode allows the fan to run continuously regardless of the compressor status. In AUTO mode, the fan status is controlled so that both the compressor and fan turn on and off simultaneously. The refrigeration system is typically comprised of a thermostat and condensing unit, as well as a circulation fan (also called an indoor fan) that functions to supply air to the conditioned space.
Over the years, engineers have worked to improve single staged refrigeration systems. Particular inventive emphasis has focused on minimizing over-sizing during the equipment selection process. Yet because cooling loads and heating loads vary substantially over the operative spectrum, these measures did not solve the excessive indoor humidity and noise levels, high energy consumption rates, and the high cost of compressor replacements and other necessary repairs often associated with the refrigeration systems.
Further development of the variable capacity compressor resulted in a more energy efficient refrigeration system with greater indoor comfort control. In this system, the compressor could modulate the cooling capacity to within a range of 15 to 100 percent.
The above mentioned development in turn led to the creation of a system comprising both a variable capacity compressor and variable frequency drive. In this new system, the fan speed and compressor capacity could be modulated to maintain the zone temperature set point and discharge air temperatures, respectively. Due to high retrofit costs, however, this system is not implemented in the millions of already existing refrigeration systems. Noise levels are still high under partial load conditions as well. US patent application 20090255278 to Lifson and Taras (2005), proposes a single integrated modulation device that controls a condenser fan, compressor, and indoor fan or, alternatively, three separate modulation devices that each control one of the three previously stated devices (condenser fan, compressor, and indoor fan at the same speed. Results from lab experiments conducted by the inventor of the proposed application suggests that modulating the condenser fan at the same speed as the compressor and indoor fan will result in a 20+ energy penalty under most operating conditions. The optimizer proposed in the following application utilizes a single modulation device to control only an indoor fan and compressor and is, therefore, more energy efficient than the device proposed by Lifson and Taras.